In modern automatic milking farms vacuum pumps supply vacuum to the milking equipment for performing necessary tasks, such as milking and washing of the equipment.
Since milking animals need to be milked with a regular interval it is necessary that the equipment is functional and longer malfunctions are not tolerated due to animal health care and for economic reasons. Therefore it is commonplace to have two separate vacuum pumps, each being capable of supplying the vacuum needed for the operation of the milking equipment, one for ordinary use and one as a back-up vacuum pump. The back-up pump should be kept operational and it is therefore important to regularly start the back-up vacuum pump for lubrication purposes, to prevent corrosion and as well to generally make sure it is working. It is of course expensive to have a back-up pump standing in case of failure of the main pump, as well as cumbersome to remember now and then to start the back-up pump.
For some jurisdictions both the operating vacuum pump and the back-up vacuum pump need to be dimensioned according to regulations requiring that every milking point in a milking parlour should have a vacuum reserve. In large milking parlours this will add up to significant vacuum reserves. When the airflow requirements are not significant the vacuum pump may be operated at a lower rotation speed. If the vacuum pump is over-dimensioned, due to regulations, this situation will occur more often than otherwise having negative effects on the vacuum pump system.
Due to the lower rotation speed pumps may be over heated due to lower airflow there through, lubrication of the pump may be insufficient, the efficiency of the motor driving the pump is low since motors are dimensioned to be optimally efficient for a particular rotation speed, the efficiency of the pump may be reduced due to for instance increased air leakage. Moreover, the vacuum pump is generally over-dimensioned resulting in increased capital cost, not to mention difficulties in handling of larger vacuum pumps.
One way of reducing these problems is to introduce so called bleeders, which will allow air into the vacuum system, thereby forcing the vacuum pump into a higher rotation speed. This, is however obviously a waste of resources.
A milking machine in a traditional milking parlour may have 6 to 50 milking points using one vacuum pump. Traditionally, a robotic milking machine serving one animal at a time uses one vacuum pump.
In larger automatic robotic milking farms two or more automatic milking robots may be serving a herd of milking animals. These automatic milking machines will then have a common, total vacuum requirement which the vacuum pumps need to be dimensioned for. Furthermore, such automatic milking machines operate in different operating modes, such as milking, equipment washing, teat cleaning and stand-by to mention a few. Each of these modes have individual vacuum requirements, where for instance equipment washing may have a high airflow at some vacuum level, and milking will have a small airflow, but requires a steady vacuum level. Thus, the vacuum pumps need to be dimension to handle a situation where all automatic milking machines are in the worst operating mode for vacuum supplying purposes. Equipment washing may in turn include a number of different washing steps, such as washing of teat cups, washing of teat cleaning cups, washing of conduits, etc. Further more, equipment washing can on one hand be a short rinsing of teat cups and conduits, which may be conducted between every animal in a milking robot, and on the other hand washing of the complete milking system, which might be done only 2 or 3 times a day.
Assuming for instance that equipment washing will result in an airflow of 500 liters/minute at an approximate vacuum level of 30 kPa, and that milking requires a steady vacuum of 45 kPa and will result in an airflow of 150 liters/minute, a system comprising two automatic milking robots being served by one single pump, the pump needs to be dimensioned to provide a steady vacuum of 45 kPa with an airflow of 650 liter/minute but also to provide an approximate vacuum level of 30 kPa and an airflow of 1000 liter/minute.
However, the two automatic milking machines are only occasionally both equipment washing or performing other high airflow operations at the same time, but are more commonly performing different tasks, where one may be less requiring. Thus, the vacuum pump must be dimensioned for a situation, which will not occur very often. A vacuum pump dimensioned accordingly will of course be expensive both in purchase and in operation.